Geodetic transit compasses have been known for many years and have been developed to a high degree of precision, reliability and durability. Such apparatus are used in military manuevers, claim staking (oil, gas, mining, etc.), determining vertical and horizontal angles, grading roads and fields, geological field work, above and below ground surveying, topographic mapping, setting timber cutting lines, use as a prismatic compass, use as a level or plumb bob, and the like. Such compasses are widely used by exploration geologists, surveyors, mining engineers, hikers, and in the military.
Exploration geologists use such devices in searching for ore deposits, etc. frequently in remote areas involving helicopter supported operations whereby the geologist is located from the air and picked up for transfer to a new work area or return to the base of operations. In for example, deep valleys and canyons, only a few seconds are provided for signalling to the helicopter from the ground, and ordinary relective devices have proven essentially unreliable for establishing contact, on the order of about a one percent (1%) success ratio, assuming the sun is shining and in line with the geologist on the ground. Attempts to use the compass mirror for such emergency signalling usually involved more than a few seconds to align and in any event was pure chance that proper alignment was even achievable within any time frame.
The United States Navy developed a generally rectangular signalling mirror for such signalling purposes utilizing a so-called diffraction sighting principle which involves a central circular aperture in the mirror having an annular rectangular wire mesh insert therein which when held to the eye with the mirrored surface facing outwardly from the eye of the observer, enabled alignment of the reflective sun's rays with a distant target such as a relatively fast moving plane or helicopter or ship in a fraction of a second with effective regularity. Such signalling mirror has also proved effective in light cloud cover or hazy weather.
The problem involved with use of such a mirror by a geologist or the like was that in deep valleys or canyons, so few seconds were available for signalling a fast moving plane or helicopter, valuable time was lost and often times the signalling opportunity was lost due to the necessity to search for and unwrap the fragile signalling mirror.
Another problem was that two separate devices were required which enhanced the possibility of misplacement or loss of the mirror. Also, the Navy-type signal mirror is very fragile and has to be carefully wrapped, therefore it is not always immediately accessible.
As will be seen hereinafter, the present invention provides a compact reliable combination of features in apparatus having utility not only for use as a geodetic compass but also as an emergency signalling mirror which is disposed in a protected but readily available condition for use.